GB1577982A - Gas discharge tubes - Google Patents

Description

PATENT SPECIFICATION

( 21) Application No 11287/78 ( 22) Filed 22 Mar 1978 (l ( 31) Convention Application No 2713702 ( 32) Filed 28 Mar 1977 in ( 11) 1 577 982 ( 33) ( 44) Fed Rep of Germany (DE) Complete Specification Published 29 Oct 1980 ( 51) INT CL 3 CO 3 C 27/02 ( 52) Index at Acceptance CIM 463 WF Hi D 35 9 C 1 A 9 C 1 X 9 C 1 Y 9 FX 9 FY 9 H 9 Y ( 54) IMPROVEMENTS IN OR RELATING TO GAS DISCHARGE TUBES ( 71) We, HEIMANN GMBH, a German Company of 6200 WiesbadenDotzheim, Weher Koppel 6, Federal Republic of Germany, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:The present invention relates to gas discharge tubes, and is applicable to flash tubes.

A gas discharge tube is known, for example, from "Philips' Technische Rundschau", 22nd Volume 1960/61, No 8, page 289-303.

It consists, in its simplest form, of a straight piece of glass tube into which an electrode is fused in gas-tight fashion, through an anode and a cathode, at respective ends Generally the anode consists of tungsten or molybdenum and the cathode consists of a sintered body comprising saturating substances composed of emission material and getter material (such as described, for example, in the German Auslegeschrift No 23 32 588) The glass envelope is filled with an inert gas, preferably xenon, on account of its spectral light distribution which is similar to that of natural daylight An ignition electrode, generally applied externally, initiates gas discharges between itself and the cathode by producing an electric field which rises very rapidly whereby that part of the gas contained in the glass envelope which part is affected by the field becomes ionised and an electrical discharge takes place This discharge extends in the direction of the anode until the filed strength of the electric field prevailing between cathode and anode has become of such magnitude that further ionisation by the electric field occurs and consequently the main gas discharge between cathode and anode is triggered The initiation of the gas discharge can also take place without a separate ignition electrode by so-called "overhead ignition", if the anode receives an adequate voltage pulse.

The glass envelope consists of quartz crystal glass or other hard glass having a very high melting point The electrode material (or at least the material of the metallic supply lines which pass through gas-tight seals into the glass envelope to the electrodes) must be matched so that differences between the thermal expansion coefficients of the supply line material and the glass envelope do not result in cracks in the gas-tight connection When hard glass is used for the envelope, this matching can be effected by selecting tungsten for the electrodes or at least for the through-going supply lines and matching the tungsten by a hard glass of an appropriate expansion coefficient Matched glass of this type is commercially available In the case of quartz crystal glass, direct matching is not possible In this case, (and also in the case where hard glass is used for the envelope but, for reasons of cost, nickel is used, for example, in place of expensive tungsten for the through-going supply lines) an intermediate body composed of a different glass must be provided in order to avoid a sudden large change in thermal expansion coefficients.

Although tungsten, in combination with matched hard glass, has the advantage incomparison to other metals that no intermediate glass is required, the cost of tungsten is relatively high and tungsten cannot be soldered The compromise of using an expensive metal which can sustain a high thermal load only for the actual electrodes and employing a sintered body for the cathode, and producing the through-going supply lines from a cheap metal necessitates an intermediate glass body This is an equally expensive solution as high-cost process steps are required.

According to the invention, there is proU 4 1 577 982 vided a gas discharge tube having a sealed glass envelope closed by a body of sintered glass through which body passes in a sealed manner at least one electrically conductive lead, the body have been cemented to the envelope without melting of either the body or the envelope.

Preferably, said envelope is closed at each of two ends thereof by a respective said body.

Preferably, the or each said body is secured to end surfaces of said envelope.

Preferably, the or each said body provides a mounting support for the tube.

The or each body may be secured to the envelope by glass solder The solder may be constituted by glass which absorbs infra red radiation, such as glass containing an iron oxide.

Where the or each body is secured by glass solder, it may additionally be secured by an adhesive It may also be secured exclusively by an adhesive, which may be organic.

The adhesive may provide an elastic support between said envelope and the or each said body.

Preferably, the or each body is constituted by glass which absorbs infra red radiation.

Preferably, the or at least one said body is formed from at least two layers having mutally differing coefficients of thermal expansion.

The or each said body may be sintered from solder glass.

Preferably, a further lead extends through the or a said sintered glass body and forms a starter electrode and/or a getter.

At least one said lead may be constituted by a Ni Fe alloy or a Ni Fe Co alloy or by molybdenum.

For a better understanding of the invention and to show how the same may be carried into effect, reference will now be made, by way of example to the accompanying drawing, in which the single Figure illustrates a gas discharge tube schematically.

The illustrated tube is of the kind that are suitable for use as flash tubes Only the ends of this flash tube have been shown These ends contain the cathode and the anode and form seals of a discharge tube shaped in accordance with the particular requirements In the simplest circumstances the tube is straight However, the tube can also be bent in U-shape or circular shape or can have more complicated forms.

An envelope l is composed of a boron silicate glass or quartz crystal in order to be both capable of withstanding a high temperature load and to be transparent Envelope 1 preferably has a circular cross-section and has annular surfaces 2 and 3 at its ends A sintered glass body 5 is secured onto the end surface 2 by glass solder 4 The glass solder can be applied to the solder surface in the form of a solder ring or by means of silk screen printing Body 5 has an external cylindrical part and a conical part which projects into the envelope 1 As the outer diameter is at least equal to the outer diameter of envelope 1, an annular shoulder is formed between the outer and inner parts of body 5 This shoulder forms a solder surface and lies opposite end surface 2 of the envelope 1 A recess 6 of rectangular cross-section extends around the outer part of body 5.

The sintered glass body 5 is composed from two layers 7 and 8 which are arranged coaxially within one another, the layer 7 holding a metallic supply line 9 which is fused in position and connected to an anode The two layers 7 and 8 have mutually different coefficients of thermal expansion.

This enables the supply line 9 to be matched thermally to envelope 1 in stages Such a continuity of matching produces less mechanical loading as a result of temperature gradients The supply line 9 preferably consists of Ni Fe alloy or a Ni Fe Co alloy An anode 10 consisting of tungsten of molybdenum is welded onto the inner end of supply line 9 In order to simplify production supply line 9 and the anode 10 can also consist of one single component, in which case molybdenum is to be preferred for reasons of cost The recess 6 serves for supporting the tube in flash equipment The length over which supply line 9 is in contact with body 5 is as large as possible The long fusion path thus formed reduces the danger of hair crack formation.

At its other end 3 and at the adjoining peripheral surface, envelope 1 is glued to an appropriately shaped sintered glass body 11 thus forming an example of an adhesive seal Otherwise, the shape of body 11 corresponds to that of body 5 However, a layered construction has not been provided in this example Also, in addition to an axially fused, metallic supply line 12 carrying a cathode 13 at its inner end, a further metallic supply line 14 is fused in and serves as an ignition electrode and/or as a getter.

Beyond this exemplary embodiment, various modifications and variations are possible In fact the design freedom regarding the shape of envelope 1 and the sintered glass bodies 5 and 11 constitutes an important advantage Even in the case of complicated shapes of the envelope 1, no separate pump connecting component is required because the pumping out operation, the introduction of the filling gas and the production of the gas-tight seal, including the insertion of the electrodes, can be carried out at one single location as consecutive processes Furth1 577 982 ermore other embodiments of electrode design are possible For example, for symmetrical gas discharge lamps the anode and cathode may be carried by the same sintered glass body, or an outer ignition electrode in the form of a wire winding (known per se) may be employed.

The sintered glass bodies can be cheaply produced mechanically Their use in place of known intermediate glass obviates the need for expensive glass blowing operations A further advantage consists in that sintered glass bodies of this kind can be produced in arbitrary shapes with accurate dimensions The supply lines which simultaneously constitute the mechanical supports for the actual electrodes, are fused into the sintered glass bodies simultaneously with the production of the sintered glass bodies The glass envelope 1 possesses an accurately dimensioned length from the start When the glass tube is sealed by the sintered glass bodies by accurately dimensioned soldering and/or glueing, the electrodes assume a clearly defined position relative to one another This enables accurate setting of the focal length, (which is a decisive factor in determining the light strength irradiated during the gas discharge) actually during the production of the gas discharge tube Furthermore, the use of glass envelopes exhibiting their final length prior to closure produces the advantage that no waste glass arises.

The fact that each sintered glass body is pre-produced allows it to be designed in such manner that it serves not only as a closing body for the glass envelope and as support for the electrode and its supply line, but also as support for the gas discharge tube itself This facilitates a precise mounting of the gas discharge tu 6 e If the sintered glass body is glued to the glass envelope to form the seal, and the degree of gluing is extended beyond a level which is necessary for sealing, it is even possible elastically to support the glass envelope.

The gas-tight connection of the sintered glass bodies to the glass envelope can either be effected by a conventional organic adhesive or by a glass solder, and it is also possible to carry out the adhesion in addition to the soldering In an advantageous embodiment, the glass solder is provided with additions which absorb infra red radiation, for example iron oxide, and can then be brought to melting point with the aid of infra red radiation.

It is also advantageous in particular in respect of a satisfactory adjustment of the focal length, to use the end surfaces of the tube ends as soldering surface or adhesive surface Further electrodes, for example, to assist starting or for gettering purposes can also be passed through the sintered glass bodies A separate starting electrode arranged on the glass tube can thus be dispensed with.

Methods of manufacturing gas discharge tubes are described in our copending appli 70 cation No 11283/78 (Serial No 1577981) in

Claims (17)

1. which there is claimed a method of manu-

   facturing a gas discharge tube, in which method at least one body of sintered glass is formed with an electrically conductive lead 75 passing through the body in a sealed manner, and a glass envelope is closed by said body to form a sealed enclosure, the body being cemented to the envelope without melting of either the body or the envelope 80 WHAT WE CLAIM IS:1 A gas discharge tube having a sealed glass envelope closed by a body of sintered glass through which body passes in a sealed manner at least one electrically conductive 85 lead, the body having been cemented to the envelope without melting of either the body or the envelope.
2. 2 A tube according to Claim 1 wherein said envelope is closed at each of two ends 90 thereof by a respective said body.
3. 3 A tube according to Claim 1 or 2 wherein the or each said body is secured to end surfaces of said envelope.
4. 4 A tube according to any one of the 95 preceding claims wherein the or each said body provides a mounting support for the tube.
5. A tube according to any one of Claims 1 to 4 wherein the or each said body 100 is secured to the envelope by an adhesive.
6. 6 A tube according to Claim 5 wherein said adhesive is organic.
7. 7 A tube according to Claim 5 or 6 wherein said adhesive provides an elastic 105 support between said envelope and the or each said body.
8. 8 A tube according to any one of Claims 1 to 4 wherein the or each said body is secured to the envelope by glass solder 110
9. 9 A tube according to Claim 8 wherein the or each said body is additionally secured by an adhesive to the envelope.
10. A tube according to Claim 8 or 9 wherein said glass solder is constituted by 115 glass which absorbs infra red radiation.
11. 11 A tube according to Claim 10 wherein said glass solder includes an iron oxide.
12. 12 A tube according to any one of the preceding claims wherein the or at least one 120 said body is formed from at least two layers having mutually differing coefficients of thermal expansion.
13. 13 A tube according to any one of the preceding claims wherein the or each said 125 body is sintered from solder glass.
14. 14 A tube according to any one of the preceding claims wherein a further lead extends through the or a said sintered glass body and forms a starter electrode and/or a 130 4 1 577 982 4 getter.
15. A tube according to any one of the preceding claims wherein at least one said lead is constituted by a Ni Fe alloy or a Ni Fe Co alloy or by molybdenum.
16. 16 A gas discharge tube substantially as hereinbefore described with reference to the accompanying drawing.
17. 17 A flash tube constructed in accordance with any one of the preceding claims.

    For the Applicants, G.F REDFERN & CO, Marlborough Lodge, 14 Farncombe Road, Worthing, West Sussex.

    Printed for Her Majesty's Stationery Office, by Croydon Printing Company Limited, Croydon, Surrey, 1980.

    Published by The Patent Office, 25 Southampton Buildings, London WC 2 A l AY, from which copies may be obtained.